Method of preparing dentures



. Aug. 8, 1939. G, w 1 5 2,168,546

METHOD OF PREPARING DENTURES Original Filed Au 6, 1954 INVENTOR mob A T TORNE Y Patented Aug. 8, 1 939 UNITED STATES PATENT OFFICE Original application August 6, 1934, Serial No. 738,612. Divided and this application July 12, 1937, Serial No. 153,120

2 Claims.

This invention relates generally to the art of dental appliances and, in particular, to an improved method of designing and manufacturing dental models and artificial partial dentures.

An apparatus for carrying out the method is claimed in application Serial No. 738,612, filed August 6, 1934, now matured into Patent No. 2,108,980 dated February 22, 1938, and entitled Dental model surveyor, the present application being a division of the earlier one.

An object of this invention is to provide a method of predetermining the best angle at which a partial denture should be inserted into position to insure that retaining clasps substantially non-resilient in action can be used. In the past it has been impossible to design a partial denture which could be inserted into position from any desired direction other than the vertical and, in a situation where the remaining natural teeth were not properly aligned a partial denture inserted vertically will leave undesirable pockets or even fail to be clasped in position firmly and non-yieldably. As a result severe strains are placed on the remaining teeth.

Another object of my invention is to provide a method of pre-studying a dental model to permit designing of a partial denture which takes advantage of all the available points of retention present in the natural teeth, no matter at what angle they may lie.

This invention is intended particularly for paralleling the undesirable undercuts of the teeth to be clasped and also for charting the positions of clasps for the various types of re movable dental restorations.

This invention will find for the operator all locations on a dental model that will retard or prevent placement of a partial removable dental restoration, and will assist the operator in the construction of a partial denture which will go into position with little or no grinding.

This invention will chart upon the teeth, markings showing their greatest diameters when in parallel relationship, assisting in the construction of a partial removable denture that will not cause undue strain upon the remaining natural teeth and will go into position without unnecessary force.

Other objects and advantages of this invention will appear in the following description and appended claims, reference being had to the accompanying drawing forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

Fig. 1 is a plan view of the device with a dental model in place for surveying.

Fig. 2 is a side elevation of the device as shown in Fig. 1.

Fig. 3 is a partial elevation showing the tool in position and performing one of its functions.

Fig. 4 is a partial elevation showing the tool performing another of its functions.

Referring to the drawing more in detail the device consists of the following parts: the main or stationary base 6 upon which is mounted the rigid, stationary and vertical post I. The post I has at its upper end a shaft 8 and a shoulder 9, the shaft 8 is in vertical relation with the top surface of the main base. The horizontal arm it is provided with an integral sleeve portion H which is adapted to fit around the shaft 8 closely enough to allow the arm [0 to swing freely about the post 1 but Without excess of play or looseness in order that the arm H3 will always remain parallel with the top surface of the base. The arm i0 is provided at the opposite end from the sleeve I! with a second sleeve I2, the hole l3 therethrough being parallel with the hole 8. Hole I3 is of a suitable size to receive a tool holder I i which is held tightly in place by means of the thumb screw which is fitted into the side of the sleeve l2. The tool holder 14 has at its lower end a chuck I6 into which may be fitted the tools IT and I8. made of metal such as steel or stainless steel, and the tool It is made of lead or carbon and is used for marking purposes. These tools are of approximately the same length and diameter and are interchangeable in the chuck [6. Both tools have one end out off square and one end 3! and 3! beveled in order to reach confined places easily. The top surface of the main base 6 is smooth and fiat. The movable base i9 is also provided with a smooth fiat surface in order that it will slide over the surface of the main base with a minimum of resistance.

In using the device a master model 2!] of the denture into which the artificial denture is. to be fitted is made in the regular manner so that an exact reproduction is produced. The master model is secured to the movable base IS with a generous amount of modeling clay or other suitable plastic substance 2|. The master model 1s first moved to a position approximately like that shown in Figs. 1 and 2. Next, a contact point upon the side of any remaining natural anterior tooth is selected in the space created by'any missing teeth. If all anterior teeth are present, select a point at the median line using the inter- The tool ll is proximal gingival space or any definite point thought most suitable at the median line between the incisal edge and interproximal gingival space. This point is marked with a lead pencil and is designated by the numeral 22 in Fig. 2. With the steel tool I! in position square cut end down in the chuck IS the thumb screw I is loosened and the height of the tool holder [4 is adjusted until the tip of the tool I! contacts the previously described, selected point. The thumb screw is then tightened securely. The point selected is called the anterior point of the tripod.

To select the other two points of the tripod slide the movable base around until the tooth upon one side of the jaw which is intended to be clasped comes beneath the tip of the tool ll. Select the point 23 on the marginal ridge on which it is desired to place the occlusal rest and mark with pencil, raise or lower the master model by manipulating the modeling clay beneath the model until the tip of the tool [1 contacts this point, meanwhile maintaining the point 22 in its previously fixed position, as by tilting the master model about point 22 as a pivot. This is the second point of the tripod. The third point 24 of the tripod is selected in the same manner as the second. During this operation the positions of the points 22 and 23 are maintained, as by manipulating the master model about an imaginary line passing through these two points. These points are then each equally distant from the surface of the main base 6 and the vertical axis of the tripod is vertical to the surface of the base 6 and parallel to the axis of the tool holder l4 and the tool ll.

With the master model in this position the mesia1 or distal undesirable undercuts are determined, filled with modeling clay as shown by the shaded portions 25 and 26 in Fig. 3, and paralleled by means of the steel tool l1. (At this stage the steel tool should'be inserted with the beveled end downward.) This is easily accomplished by loosening the thumb screw and lowering the surveying arm and by sliding the movable base [9 upon the surface of the main base 6 and by swinging the surveying arm [4 and its tool 11 from side to side in order to reach all points of the teeth to be clasped.

After paralleling the undesirable undercuts the master model is removed and a duplicate casting model 2! (Fig. 4) is made therefrom. The duplicate casting model is identical in every respect to the master model except the undesirable undercuts are removed.

This casting model is mounted on the clay 2| and tripoded in the same manner as was the master model. After the casting model has been tripoded the carbon tool I8 is substituted for the steel tool ll, beveled end downward, and is used to determine and mark lines showing the greatest diameters of the teeth to be clasped when they are in parallel relationship. The vertical sides of the carbon are used to mark upon the teeth as illustrated in Fig. 4. The heavy lines 28 and 29 indicate the height of the lines of greatest diameters of the teeth to be clasped when in parallel relationship,

These lines will definitely establish all positions where clasps should be placed. The denture is then made by any one of the several methods.

In amplification of the description of the tripoding operation, that is the operation in which the three points of reference are determined, it will be described more fully. In some cases it may be desirable to conduct preliminary surveying operations to determine which is the best direction from which the partial denture should be introduced into position. In this operation the model is manipulated on its relatively high mass of modeling clay or other suitable material to select the desirable undercuts and to insure that undesirable undercuts will not be present. In this operation the model is, in effect, tilted about a plurality of fulcrum points due to the amount of movement made possible by the depth of the modeling clay.

A further accomplishment of this preliminary step is to make possible the creation of special undercuts which cannot be created when the model is moved about a single fulcrum point.

In selecting the three points of reference after this preliminary surveying step, it is important that they be located as far apart as possible to determine a coarse or easy adjustment upon the casting model. This is done in the manner previously set forth.

I claim:

1. In the process of manufacturing cast partial dentures the steps of setting a master model in a position with respect to a vertical line therethrough such as to modify undercuts in the model, filling in selected undercuts with a plastic, smoothing the outer surfaces of the plastic into parallelism with said vertical line, and making a duplicate model from said plastic-filled master model.

2. In the process of preparing a denture model for the reception and retention of a partial denture, the steps which include mounting a master model in movable juxtaposition to a surveying instrument, moving the model during the surveying process to locate undercuts suitable and unsuitable for retention of the denture, filling in the unsuitable undercuts, and preparing a duplicate model of said filled-in master model.

NOBLE G. WILLS. 

